1. Field of the Invention
The present invention relates to a separation type optical pickup device.
2. Description of the Related Art
An example of the separation type optical pickup device is described hereinafter.
First, within a fixed optical system unit having a light emission system disposed in the fixed system unit, a laser beam emitted from a laser diode is collimated by a coupling lens and passes through a polarization beam splitter and a quarter-wave plate to reach a deflection prism. The beam deflected by the deflection prism impinges to a tracking mirror which deflects the beam again to output the beam out of the fixed unit toward a movable optical system unit.
The beam entered in the movable unit is deflected by a deflection prism mounted on the movable system and guided to an objective lens which converges the beam on an optical disk surface to form a minute spot thereon so as to read/write information from or in the disk.
The beam is reflected on the disk surface. The reflection beam reflected from the disk surface is collimated by the objective lens and guided back to the fixed optical unit. The reflection beam is deflected in the fixed unit by the tracking mirror and then by the deflection prism and enters in the polarization beam splitter after passing through the quarter-wave plate. In this event, the polarization direction of the reflection beam to be entered into the beam splitter is rotated by 90 degrees from the beam at the time of emission from the laser source. Therefore, the beam is deflected by the beam splitter and guided to a signal detection optical system. In the detection system, the beam is converged by a condenser lens and passes through a cylindrical lens which generates astigmatism in the beam, whereby it becomes possible to detect information data recorded in the disk, a focus error signal and a track error signal from the reflection beam by a photo detector.
The separation type optical pickup device mentioned above comprises a tracking actuator housed in the fixed unit for adjusting the tracking mirror. The pickup device also comprises a focus actuator housed in the movable unit for driving and adjusting the objective lens along the direction of the optical axis thereof.
In accordance with the optical pickup device mentioned above, if the optical axis of the beam output from the fixed unit to the movable unit is not accurately aligned with the moving direction of the movable unit, the optical axis of the beam received by the photo detector is shifted depending on the seeking position of the movable unit. Also, if the optical axis of the beam is dislocated from the center of the objective lens after passing through the deflection prism in the movable unit, the track error signal detected by the photo detector is offset due to the dislocation of the optical axis of the beam. Therefore, it is necessary to adjust the optical elements so that the optical axis of the beam transmitted from the fixed unit to the movable unit is strictly in parallel to the moving direction of the movable unit and coincides with the center axis of the objective lens.
For that purpose, the tracking actuator is arranged to adjust the tracking mirror by shifting and rotating the mirror so as to correct the optical axis of the beam incident to the objective lens along the direction of X-axis and control the optical axis of the beam transmitted from the fixed unit about the Y-axis.
Also, in that case, the optical axis of the beam incident to the objective lens is adjusted along the direction of Y-axis by moving whole of the optical output system including the laser diode and the coupling lens along the Y-axis. Further, the optical axis of the beam transmitted from the fixed unit is adjusted about the Z-axis by shifting the laser diode with respect to the coupling lens along the direction of Y-axis.
However, in accordance with the above-mentioned way of adjusting the optical axis of the beam, the adjusting mechanism is directly provided on the tracking actuator which drives the tracking mirror as a result of which the actuator becomes bulky.
Besides, in accordance with the adjusting way, it becomes necessary to individually adjust apart from each other the inclination, location and alignment along the X-axis and Y-axis with respect to the optical axis of the beam incident to the objective lens and the optical axis of the beam transmitted from the fixed unit. Therefore, a problem arises wherein the adjustment results interfere with each other so that when the optical axis inclination along one direction is adjusted and after that the optical axis inclination along another direction is adjusted, the optical axis along the first direction becomes dislocated again from the position where it should be.